As such an image acquisition device, there is a light-sheet microscope that irradiates sheet-like excitation light to a sample and captures detection light emitted from the sample in association with irradiation of the excitation light (see, for example, the following Non-Patent Literature 1). In the light-sheet microscope described in Non-Patent Literature 1, it is possible to produce pseudo sheet-like excitation light by generating a Bessel beam by a spatial light modulator (SLM) and scanning a light focus point of the generated Bessel beam along its optical axis.